Littelfuse MPU Series Modules

Technical Dossier

Product Details And Specifications

Littelfuse MPU Series: Comprehensive Module Range and Technical Overview

The Littelfuse MPU (Motor Protection Unit) Series represents a purpose-engineered family of modular motor protection relays deployed across global heavy industry sectors including petrochemical plants, offshore platforms, nuclear auxiliary systems, and refinery motor control centers (MCCs). With installations spanning IEC and ANSI protection environments, the MPU Series has established a significant installed base in applications requiring ANSI functions 46, 48, 49, 50, 51, 66, and 86 within a single compact chassis. Its modular I/O architecture allows plant engineers to configure protection and monitoring functions without replacing the base unit, reducing both downtime and spare parts inventory complexity.

The Evolution of MPU Series Architecture

The Littelfuse MPU Series originated from the POWR-GARD product line, which Littelfuse acquired through its purchase of ESCO Technologies' relay division. Early-generation MPU units (MPU-32 platform) used discrete analog input cards with RS-485 Modbus RTU as the primary communications interface. These units were designed for standalone MCC bay deployment with limited SCADA integration capability.

The second-generation MPU architecture introduced a modular backplane system, separating the CPU module from analog input, digital input, and communications adapter modules. This allowed field-upgradeable firmware and hot-swap-compatible I/O expansion without full relay replacement. The MPU-32 evolved into the MPU-32E with expanded event logging (up to 1,024 events) and enhanced harmonic analysis capability up to the 31st harmonic.

Current-generation MPU modules support dual-port Ethernet with EtherNet/IP and Modbus TCP protocols, enabling direct integration with Rockwell Automation ControlLogix and Siemens S7 PLC environments. Compatibility issues arise when mixing first-generation analog input modules (MPU-AIM-xx-xx) with third-generation CPU modules due to backplane register map changes introduced in firmware v3.x. Plants operating mixed-generation MPU fleets must maintain firmware version discipline across all chassis slots.

MPU Series Full Catalog & Functionalities (SKU List)

Current Input Modules (CIM)

• MPU-CIM-00-00: Standard 3-phase current input module, 1A/5A CT secondary, no ground fault
• MPU-CIM-01-00: 3-phase current input module with dedicated ground fault CT input channel
• MPU-CIM-02-00: 3-phase current input with residual ground fault calculation, no external GF CT required
• MPU-CIM-00-01: Standard current input module with RTD input expansion port enabled

Analog Input Modules (AIM)

• MPU-AIM-00-00: 6-channel RTD input module, PT100/PT1000 compatible, Celsius/Fahrenheit selectable
• MPU-AIM-01-00: 10-channel RTD input module for high-density thermal monitoring applications
• MPU-AIM-02-00: 4–20 mA analog input module, 4 channels, process variable monitoring

Digital Input/Output Modules (DIM / DOM)

• MPU-DIM-00-00: 8-channel 24 VDC digital input module, optically isolated, status monitoring
• MPU-DIM-01-00: 16-channel digital input module, 120 VAC compatible, extended voltage range
• MPU-DOM-00-00: 6-channel relay output module, Form C contacts, 5A @ 250 VAC rated
• MPU-DOM-01-00: 4-channel high-current relay output module, 10A @ 250 VAC, trip-duty rated

CPU / Base Modules

• MPU-32: Base CPU module, RS-485 Modbus RTU, 512-event log, standalone operation
• MPU-32E: Enhanced CPU module, dual RS-485, 1024-event log, harmonic analysis to 31st
• MPU-32E-ETH: CPU module with dual-port EtherNet/IP and Modbus TCP, SNTP time sync

Communications Adapter Modules

• MPU-CAM-00-00: DeviceNet communications adapter, Group 2 slave, 500 kbps max
• MPU-CAM-01-00: PROFIBUS DP adapter module, 12 Mbps, GSD file provided
• MPU-CAM-02-00: EtherNet/IP + Modbus TCP dual-protocol adapter, 100 Mbps

Power Supply Modules

• MPU-PSM-00-00: 24 VDC auxiliary power supply module, 20W output, DIN rail mount
• MPU-PSM-01-00: 120/240 VAC universal input power supply module, 30W, wide-range input

Sourcing Hard-to-Find & Obsolete MPU Series Parts

The MPU-32 base platform and first-generation CIM/AIM modules have reached end-of-active-production status. Littelfuse no longer manufactures replacement units for the MPU-32 (non-E) CPU module or the MPU-CAM-00-00 DeviceNet adapter. Plants operating these units face a sourcing gap that standard distribution channels cannot fill.

DriveKNMS maintains a dedicated inventory of tested MPU Series modules sourced from decommissioned MCC panels, plant shutdowns, and authorized surplus channels. Each unit undergoes functional verification before listing. For facilities requiring long-term maintenance contracts covering MPU Series spares, DriveKNMS provides multi-year supply agreements with guaranteed stock reservation. This service is specifically structured for refineries and chemical plants operating under 10–20 year asset lifecycle plans where relay replacement with a modern equivalent is not operationally feasible in the short term.

Quality Control for the MPU Series Range

MPU Series modules use a proprietary backplane bus operating at 5 VDC logic levels with differential signal pairs for inter-module communication. Standard bench testing with generic relay test sets is insufficient to validate backplane integrity. DriveKNMS applies the following test protocol to all MPU modules:

• Backplane bus continuity and impedance verification using MPU-compatible chassis fixture
• CT input accuracy test: inject calibrated 1A and 5A secondary signals, verify metering accuracy within ±0.5% of rated
• RTD channel verification: apply decade resistance box at PT100 reference values (0°C = 100Ω, 100°C = 138.5Ω), confirm displayed temperature within ±1°C
• Digital I/O functional test: cycle all input channels with 24 VDC test signal, verify output relay actuation and contact resistance <100 mΩ
• Communications loopback test: Modbus RTU register read/write verification across all defined function codes
• Firmware version identification and documentation prior to shipment